An internal combustion engine generates power by burning fuel in a combustion chamber in an air media drawn into the chamber. Intake valves are operated by a camshaft in order to intake the air, and the air is drawn into the combustion chamber while the intake valves are open. In addition, exhaust valves are operated by the camshaft, and a combustion gas is exhausted from the combustion chamber while the exhaust valves are open.
Optimal operation of the intake valves and the exhaust valves depends on a rotational speed of the engine. That is, an optimal lift or optimal opening/closing timing of the valves depends on the rotational speed of the engine. In order to achieve such optimal valve operation depending on the rotational speed of the engine, various research, such as designing of a plurality of cams and a continuous variable valve lift (CVVL) that can change valve lift according to engine speed, has been undertaken.
Also, in order to achieve such an optimal valve operation depending on the rotational speed of the engine, research has been undertaken on a continuously variable valve timing (CVVT) apparatus that enables different valve timing operations depending on the engine speed. The general CVVT may change valve timing with a fixed valve opening duration.
However, the general CVVL and CVVT are complicated in construction and are expensive in manufacturing costs.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.